The present invention relates to video data compression, and more particularly, to the compression of video data for transmission at greatly reduced data rates. The invention is advantageous for the transmission of real-time video images through telephone lines.
A video compression system reduces the amount of data required to reproduce or duplicate an original image or picture. In existing video compression techniques, such as those described in U.S. Pat. Nos. 4,816,901, 4,847,677, 4,849,807 and 4,914,508, a frame of digital video data is compressed and encoded line-by-line in real time by determining points along each video line. The selected points are points of inflection that convert the video line into a series of linear segments, the points representing the end-points of the linear segments. When converted back to digital data, the points generate an acceptable reproduction of the original line.
One video compression technique disclosed in the above-identified patents requires the length between selected of a linear segment to be least 2 pixels but not more than 17 pixels. Unfortunately, this compression technique results in the selection of an excessive number of points in picture areas of rapid slope changes and picture quality suffers in areas of very flat, or low slope changes. For example, in a picture having a vertical line or sharp contrast edge, the two pixel minimum requirement results in a relatively random jagged line when the edge is located generally between horizontal pixels. Also, in a picture having a uniform picture area, i.e., a picture having very flat or low slope areas resulting in long pixel lengths between points, the line-to-line pointing location often appears random and image quality suffers.
Accordingly, there exists a definite need for video compression techniques for providing good edge definition and for providing good picture quality in regions of picture uniformity. The present invention satisfies these needs and provides further related advantages.